An alkylation process, which is disclosed in U.S. Patent Application Publication 2006/0131209 (“the '209 publication”), involves contacting isoparaffins, preferably isopentane, with olefins, preferably ethylene, in the presence of an ionic liquid catalyst to produce gasoline blending components. The contents of the '209 publication are incorporated by reference herein in its entirety.
An ionic liquid catalyst distinguishes this novel alkylation process from conventional processes that convert light paraffins and light olefins to more lucrative products such as the alkylation of isoparaffins with olefins and the polymerization of olefins. For example, two of the more extensively used processes to alkylate isobutane with C3-C5 olefins to make gasoline cuts with high octane numbers use sulfuric acid (H2SO4) and hydrofluoric acid (HF) catalysts.
Ionic liquid catalysts specifically useful in the alkylation process described in the '209 publication are disclosed in U.S. Patent Application Publication 2006/0135839 (“the '839 publication”), which is also incorporated by reference in its entirety herein. Such catalysts include a chloroaluminate ionic liquid catalyst comprising a hydrocarbyl substituted pyridinium halide and aluminum trichloride or a hydrocarbyl substituted imidazolium halide and aluminum trichloride. Such catalysts further include chloroaluminate ionic liquid catalysts comprising an alkyl substituted pyridinium halide and aluminum trichloride or an alkyl substituted imidazolium halide and aluminum trichloride. Preferred chloroaluminate ionic liquid catalysts include 1-butyl-4-methyl-pyridinium chloroaluminate (BMP), 1-butyl-pyridinium chloroaluminate (BP), 1-butyl-3-methyl-imidazolium chloroaluminate (BMIM) and 1-H-pyridinium chloroaluminate (HP).
However, ionic liquid catalysts have unique properties making it necessary to further develop and modify the ionic liquid catalyzed alkylation process in order to achieve superior gasoline blending component products, improved process operability and reliability, reduced operating costs, etc. For example, as a result of use, ionic liquid catalysts become deactivated, i.e. lose activity, and may eventually need to be replaced.
Alkylation processes utilizing an ionic liquid catalyst form by-products known as conjunct polymers. These conjunct polymers can deactivate the ionic liquid catalyst by forming complexes with the ionic liquid catalyst. Conjunct polymers are highly unsaturated molecules and may complex the Lewis acid portion of the ionic liquid catalyst via their double bonds network system. As the aluminum trichloride becomes complexed with conjunct polymers, the activity of the ionic liquid becomes impaired or at least compromised. Conjunct polymers may also become chlorinated and through their chloro groups may interact with aluminum trichloride and therefore reduce the overall activity of the catalyst or lessen its effectiveness as a catalyst for the intended purpose such as alkylation. Deactivation of the ionic liquid catalyst by conjunct polymers is not only problematic for the alkylation chemistry, but also weighs in heavily on the economics of using ionic liquids because they are expensive catalytic systems and their frequent replacement will be costly. Therefore, commercial exploitation of ionic liquid catalysts during alkylation is impossible unless they are efficiently regenerated and recycled.
U.S. patent application Ser. No. 12/003,578 (“the '578 application) is directed to a process for regenerating an ionic liquid catalyst which has been deactivated by conjunct polymers. The process comprises the steps of (a) providing an ionic liquid catalyst, wherein at least a portion of the ionic liquid catalyst is bound to conjunct polymers; (b) reacting the ionic liquid catalyst with aluminum metal to free the conjunct polymers from the ionic liquid catalyst in a stirred reactor or a fixed bed reactor; and (c) separating the freed conjunct polymers from the catalyst phase by solvent extraction in a stirred or packed extraction column. The contents of the '578 application are incorporated by reference herein in their entirety.
In order to provide regenerated ionic liquid catalyst, in the process of the '578 application, spent ionic liquid catalyst reacts with aluminum metal. If the spent ionic liquid catalyst is a chloroaluminate ionic liquid catalyst, such as catalysts disclosed in the '839 publication, it produces aluminum trichloride (AlCl3) as a byproduct. The AlCl3 byproduct can remain dissolved in the regenerated catalyst. Accordingly, it is necessary to separate the regenerated catalyst and the AlCl3 byproduct so that the regenerated catalyst can be recycled to the alkylation step.
Therefore, there is a need for an effective and efficient process for removing metal halides from an ionic liquid catalyst, and, in particular, a regenerated ionic liquid catalyst. In general, the process should be simple and efficient enough to be used to separate any metal halide from an ionic liquid.